/Engine/Source/Runtime/MediaUtils/Public/IMediaPlayerLifecycleManager.h
The low level player instance release resources. This callback receives a bitmask of possible resource types (Resource_Flag...) to allow proper tracking of players that release certain types of resources at different times. Some players will issue this callback asynchronously, it may hence be triggered long (100-200ms are possible) after the closing or destruction of a player.
class IMediaPlayerLifecycleManagerDelegate